Root caries will become an even greater cause of tooth loss in mature and aging individuals in the near future than in the recent past because of successful prevention of enamel decay and tooth loss in the relatively young. The objective of this research is to develop an effective fluoride formulation for safe-self application by the aging population for prevention of root and coronal caries. The focused specific aims are oriented for rapidly fulfilling this objective by (a) confirming the known information of fluoride effects on root surface tissue; and (b) development of a new mode of fluoride incorporation in the tissue which preliminary results indicate is highly effective against in vitro root caries. Aims are to determine in an in vitro root caries model; (1) lack of effect of the same ambient F- which is effective for enamel, (2) mechanisms of effective F- incorporation by recyrstallization of root tissue, (3) parameters of optimum formulation and application for maximum effectiveness. Additional aims are to test the best formulation(s) in a bacterial root caries model and in situ in two human subjects on tooth tissue cemented in a prothesis. Topical fluoride formulations now in clinical usage will be evaluated for beneficial and harmful effects on root tissue. Data will be derived by determining mineral ion flux (Ca, PO4, and F) between the tissue and environment, tissue mineral analyses (Ca, PO4, Mg and F), microradiographically, light microscopy, electron microscopy and X-ray diffraction. Interpretations will be made of effects of fluoride on demineralization, remineralization, recyrstallization, and other noted tissue changes. Results of these studies will add considerably to the small amount of information available of fluoride reactions with human root tissue. Rapid availability of these new facts will aid in maintenance of human health and welfare.